Exposure method and exposure apparatus

ABSTRACT

The invention deals with an exposure apparatus which detects environmental conditions such as atmospheric pressure, temperature and humidity in which the exposure apparatus is placed, and which maintains the projected magnification constant at all times based upon the detected values, so that the pattern can be reproduced precisely. Concretely, the apparatus comprises a detector to detect at least one of the tube temperature of the optical projecting system, humidity or atmospheric pressure near the optical system, and a control unit which controls optical characteristics based upon the signals detected by the detector. Namely, the control unit adjusts the optical characteristics depending upon the environmental conditions thereby to adjust variation in the projecting magnification and/or variation in the focal position. Thus, variation in the optical characteristics is adjusted to transfer the pattern maintaining high precision.

BACKGROUND OF THE INVENTION

The present invention relates to an exposure method and an exposureapparatus which will reproduce patterns very precisely by adjusting suchoptical characteristics as magnification, focal distance and the likecaused by the changing environmental conditions such as atmosphericpressure, temperature and humidity.

Photolithography is generally utilized in the manufacture ofsemiconductor devices such as IC's and LSI's, and patterns for reticlesand photomasks are transferred onto the surfaces of an originalphotomask board and semiconductor wafer relying upon photographictechniques. A recent tendency has been to further reduce the size ofpattern to be transferred accompanying the trend toward fabricatingsmaller element patterns for semiconductor devices in toward fabricatingsemiconductor devices more densely. Therefore, an exposure apparatus ofthe type of with a reduction proportion of 1:5, (or reduction ratio of1/5) or deduction proportion of 1:10 (or reduction ratio of 1/10) hasbeen much used in optical systems for transferring patterns.

A widely known exposure apparatus used for the manufacture ofsemiconductor devices has been disclosed in a journal Denshi Zairyo, Y.Kamata, S. Nakase, "Light Exposure Apparatus", November, 1983, separatevolume, pp. 97-104, esp. pp. 97-98.

SUMMARY OF THE INVENTION

The inventors have attempted to transfer a variety of patterns using theexposure apparatus of this type, and have found that the reduction ratioof the pattern transferred, varied slightly depending from day to dayand that the focal position also varied slightly. This variationoccurred even when ambient temperature and humidity in a clean room inwhich the exposure apparatus was installed, were maintained constant, oreven when an attempt was made to stabilize the wavelength of light fromthe light source.

The inventors therefore have conducted experiments extensively to findthe cause of variation in the reduction ratio, and have arrived at thefollowing conclusion. The inventors measured the daily change in thereduction ratio as well as the atmospheric pressure. A correlation wasfound as shown in FIG. 1 wherein the abscissa represents atmosphericpressure (January to February, 1984, Tokyo) and the ordinate representsthe reduction ratio. Having plotted a number of data (only part of thedata is plotted in FIG. 1(a), it was found that a correlation roughlygiven by a linear equation is established, i.e., atmospheric pressure Pand the change of reduction ratio M satisfy a relation M=Kp×P+Cp, whereKp and Cp denote constants determined by the characteristics of theoptical system. Further, the reduction ratio M is defined in terms ofthe change in size relative to a pattern size of 13.5 mm as shown inFIG. 1(b). Namely, M=1/8(ΔA_(X) +ΔA_(Y) +ΔB_(X) +ΔB_(Y) +ΔC_(X) +ΔC_(Y)+ΔD_(X) +ΔD_(Y)).

The inventors have furthered the study concerning the relation betweenthe change in the reduction ratio and the atmospheric pressure to find acorrelation between changes in the atmospheric pressure in the cleanroom (chamber) accompanying changes in ambient atmospheric pressureoutside the chamber, changes in the reduction ratio, and changes in thefocal position. It was found as shown in FIGS. 2 and 3 that the samecorrelation existed between the pressure in the clean room and thechange in the reduction ratio just as under ambient atmospheric pressureoutside the clean room, and that the same correlation existed withrespect to the focal point though there existed some width in the changeof the focal point.

The pressure in the clean room is maintained so as to be slightly higher(by about 1 mb) than the atmospheric pressure in order to prevent dustand dirt in the atmosphere outside from infiltrating the clean room.

The inventors have further repeated experiments extensively to discussthe cause of change in the reduction ratio (transfer magnification), andhave found that the reduction ratio was directly affected bytemperature, humidity, and atmospheric pressure of the environment inwhich the apparatus was installed.

That is, the tube in the optical projection system expands or contractsas temperature changes, and sizes of optical axes of reticle and lenschange, thereby changing the reduction ratio. Moreover, moisture densityof the air changes with humidity in the optical projection system, sothat the relative refractive index of the lens changes so that thereduction ratio changes accompanying the focal distance.

Based upon the results discussed by the inventors, the object of thepresent invention is to provide an exposure method and an apparatustherefor, in which change in the projecting magnification such asreduction ratio of the transferred pattern and the change in the focalposition, are adjusted independently of the change in the environmentalconditions such as ambient atmospheric pressure, temperature, humidityand the like, to improve dimensional precision of the transferredpattern and to improve alignment precision, so that the pattern can bereproduced very precisely.

The above and other objects as well as novel features of the presentinvention will become obvious from the description of the specificationand the accompanying drawings.

A representative example of the invention disclosed in this applicationwill be briefly described below.

That is, the atmospheric pressure of the environment in which theexposure apparatus is placed is detected, the atmospheric pressure beingsubject to change depending upon the change in the external ambientatmospheric pressure, and the optical characteristics of the opticalprojecting system are controlled to remain substantially constantresponsive to the change in the atmospheric pressure thereby to adjustvariation in the projecting magnification and/or variation in the focalpoint, so that the pattern can be reproduced very precisely.

The optical characteristics can be controlled so as to remain constantby moving part of the optical projection system toward the direction ofoptical axis depending upon the change in atmospheric pressure, or bycontrolling the gaseous composition which is filled in the opticalprojection system.

More concretely, the method of controlling optical characteristicscomprises a pressure gauge for detecting the atmospheric pressure of theenvironment in which the exposure apparatus is placed, a light pathlength setting portion for moving part of the optical projection systemtoward the direction of optical axis, and a control unit for controllingthe light path length setting portion based upon a value detected by thepressure gauge. Further, the light path length setting portionconstitutes a gas supply system to supply a required gas into theoptical projection system, and the control unit controls the gas supplysystem to change the gaseous composition in the optical projectionsystem.

According to the present invention, furthermore, environmentalconditions such as temperature and humidity are detected in addition tothe atmospheric pressure, and the projecting magnification is maintainedconstant at all times based upon the detected values, in order totransfer the pattern maintaining high precision.

More concretely, the invention comprises detectors to detect thetemperature of the tube of the optical projection system, and to detectthe humidity and pressure near the optical system, and a control unitwhich controls optical characteristics based upon the signals detectedby the detectors. The control unit adjusts the optical characteristicsdepending upon the environmental conditions thereby adjusting variationin the projecting magnification and/or variation in the focal position,i.e., to adjust variation in the optical characteristics, so that thepattern can be reproduced very precisely.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a) and 1(b) to FIG. 3 are graphs illustrating the correlationbetween the atmospheric pressure and the projecting magnification, andbetween atmospheric pressure and focal position;

FIG. 4 is a view showing the whole construction of an embodiment 1according to the present invention;

FIG. 5 is a view showing a major portion on an enlarged scale;

FIG. 6 is a plan view showing a major portion;

FIG. 7 is a view showing the whole construction of an embodiment 2;

FIG. 8 is a view showing a major portion on an enlarged scale; and

FIG. 9 is a view showing the whole construction of an embodiment 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS [Embodiment 1]

FIGS. 4 and 5 illustrate an exposure apparatus according to anembodiment of the present invention, wherein reference numeral 1 denotesan exposure body of an exposure apparatus which is equipped with anilluminating optical system 4 having a light source 2 and a condenserlens 3, and a optical projection system 7 having a pattern to bereproduced such as mask or reticle 5 illuminated by the illuminatingoptical system 4 and a lens group 6 for projecting and forming thepattern. Further, though details are not described, the exposure body 1is equipped with an optical system 8 for setting the focus (focal point)of the projected image or for setting the alignment (position on aplane). As shown in FIG. 5 (which is a section view along the line A--A'of FIG. 6) on an enlarged scale, the projecting optical system 7 has areticle support frame 10 mounted on the upper end of the tube 9 of whichthe lower portion is fitted to a frame 11. As shown in a plan view ofFIG. 6, the reticle support frame 10 is attached to a resilient ring 12at two points P₁, P₂, and is further attached at two points P₃, P₄ tothe tube 9 via the resilient ring 12. Owing to the resilient ring 12that undergoes resilient deformation, therefore, the reticle supportframe 10 is allowed to move slightly in the direction of the opticalaxis relative to the tube 9. At three circumferential points P₅, P₆ andP₇, piezo-electric elements 16 are interposed in the direction ofoptical axis between the reticle support frame 10 and the adjustingscrews 13 screwed into the tube 9 via balls 14, 15. The piezo-electricelements 16 are provided with electrodes to which lead wires 17 areconnected. The electric current is supplied through the lead wires 17 sothat the piezo-electric elements will undergo expansion or contractionin the direction of the optical axis depending upon the amount ofcurrent.

Further, the tube 9 equipped with the lens group 6 is allowed to movewith respect to the frame 11 in the direction of the optical axis. Forthis purpose, a mechanism is employed consisting of a screw shaft 19turned by a motor 18 mounted on the frame 11, and a nut 20 which isprovided on the tube 9 and which engages the screw shaft 19. As thescrew shaft 19 turns, the lens group 6 and the reticle support frame 10move in the direction of the optical axis. Thus, the structure relatedto the reticle support frame 10 and the structure related to the lensgroup 6 constitute a light path length setting portion that sets thedistance among the reticle 5, the lens group 6 and the wafer that willbe described later, i.e., that sets the length of the light path.

An X-Y table 21 is disposed under the exposure body 1. A semiconductorwafer 22 is mounted on the X-Y table 21. The wafer 22 is placed on aposition on which a pattern of the reticle 5 will be projected on areduced scale.

A barometer 23 is installed in the environment or, generally, in a cleanroom in which the exposure body 1 and the X-Y table 21 are placed, and acontrol unit 24 is provided to control the light path length settingportion based upon the signals detected by the barometer 23. The controlunit 24 comprises a projecting magnification correction operationcircuit 25, a magnification driver 26, a focal position correctionoperation circuit 27, and a focal point driver 28, and controls theamount of electric current that flows into the piezo-electric elements16 and to the motor 18 depending upon the atmospheric pressure of theenvironment as measured by the barometer 23.

According to the above-mentioned construction, the focal point is setand the alignment is set by an automatic control mechanism in which theoptical system 8 serves as a chief element. In addition to the above,however, the pressure in the environment is detected by the barometer23. When the measured atmospheric pressure is lower than the expectedatmospheric pressure, the density of the air is reduced, the focaldistance of the lens group 6 decreases substantially, the projectingmagnification of the projected pattern decreases substantially, and thevalue for focal position is less. Therefore, the projectingmagnification correction operation circuit 25 calculates a correcteddimension based upon correlations shown in FIGS. 1 and 2 to reduce thedistance between the lens group 6 and the reticle 5, so that the samemagnification is obtained. The circuit 25 then operates themagnification driver 26 based upon the corrected dimension. Owing to thefunction of the magnification driver 26, a predetermined current flowsinto the piezo-electric elements 16 which then contract (or expand). Asthe piezo-electric elements 16 contract, the reticle support frame 10moves downward relative to the tube 9, whereby the distance between thereticle 5 and the lens group 6 is maintained constant, i.e., theprojecting magnification is maintained substantially constantirrespective of the change in the atmospheric pressure. Furthermore, thefocal position correction operation circuit 27 calculates a correctionquantity for the focal position relying upon the atmospheric pressure,and whereby the focal point driver 28 is operated to drive the motor 18.The lens group 6 then moves in the axial direction so that the focalposition is maintained substantially constant. When the detectedatmospheric pressure is higher than the expected atmospheric pressure,the reticle 5 and the lens group 6 move in the reverse direction, sothat the magnification and the focal position are maintainedsubstantially constant.

Thus, the magnification and focal position can be maintainedsubstantially constant at all times between the reticle 5, lens group 6and wafer 22 in the optical projection system irrespective of the changein the atmospheric pressure or in the atmospheric pressure of theenvironment such as the clean room in which the exposure apparatus isplaced. Hence, the projecting magnification is prevented from varyingand is stabilized, enabling the pattern to be reproduced very precisely.Since the magnification is stabilized, and the focal position is set toan optimum position, it is evident that the pattern is projected in away that insures stable and precise reproduction.

[Embodiment 2]

FIGS. 7 and 8 illustrate another embodiment of the present invention,wherein the same portions as those of the above-mentioned embodiment aredenoted by the same reference numerals. In this embodiment, the reticlesupport frame 10 of reticle 5 is secured to the tube 9 and the lower endof the tube 9 is stretched so as to come close to the surface of thewafer 22 on the X-Y table 21.

A gas intake port 30 and a gas exhaust port 31 are opened in the tube 9between the reticle 5 and the lens group 6, and a gas intake port 32 isopened in the lens tube under the lens group 6. A gas supply pipe 33 isconnected to these gas intake ports 30, 32. The gas is also suppliedinto the tube among the lenses 6. In this embodiment, furthermore, thegas supply pipe 33 is connected to a nitrogen source 34 and to an oxygensource 35. Values 36, 37 for controlling the gas flow rate are insertedin the pipe 33 to control the flow rates of gases supplied to the gassupply pipe 33. In order to adjust the temperature and humidity ofgases, an adjusting unit 50 is inserted in the gas supply pipe 33.Further, a filter 51 is inserted in the gas supply pipe 33 to clean thegases. The gases which have passed through the adjusting unit 50 areadjusted to have a predetermined temperature and a predeterminedhumidity, and are introduced into the tube 9. Therefore, the temperatureand humidity of gaseous atmosphere in the tube 9 can be adjusted todesired values. Further, since the gases that have passed through thefilter 51 have been cleaned, foreign matter is suspended in very smallamounts in the gaseous atmosphere in the tube 9. Therefore, opticalcharacteristics are not adversely affected by foreign matter in thegaseous atmosphere that serves as a light path in the tube 9.

The gas supply system from the gas sources 34, 35 to the gas intakeports 30, 32 or the gas exhaust port 31, works to control the gaseouscomposition in the optical projection system 7; hence, substantiallyserves as a light path length setting portion to set the length of thelight path.

A barometer 23 is installed near the exposure body 1 to detect theatmospheric pressure of the environment, and further, a control unit 38is provided to control the valves 36, 37 in response to the detectedatmospheric pressure, so that the flow rates of gases are controlled Thecontrol unit 38 contains circuit 39 which calculates the density of theair that varies with the change in the atmospheric pressure. In responseto output of the circuit 39, the degree of opening of the valves 36, 37is adjusted to control the flow rates of gases.

According to this construction, therefore, the nitrogen and oxygen fromthe gas sources 34, 35 are introduced into the tube 9 through gas supplypipe 33 and gas intake ports 30, 32, and are discharged through gasexhaust port 31 and the clearance between the wafer 22 and the tube 9.Therefore, the tube 9, i.e., the projecting optical system 7 is filledwith a gaseous mixture consisting of nitrogen and oxygen, the pressurethereof being equal to, or slightly higher than, the outside ambientatmospheric pressure. The refractive index of light (D-ray having awavelength of 589.3 nm) of a sodium lamp is 1 in a vacuum, 1.000292 inair, 1.000297 in the nitrogen, and 1.000272 in the oxygen. By mixingthese gases at a suitable ratio, therefore, the refractive index of thegaseous atmosphere can be controlled.

Therefore, if the density of the air changes with the atmosphericpressure of the environment, densities (relative to the air) of thenitrogen and oxygen change, too, resulting in the changes in thedensities of gases in the projecting optical system 7. Accordingly, therefractive index changes and the projection magnification changes. Thebarometer 23 however, detects the change in the atmospheric pressure,and degree of opening of the control valves 36, 37 is adjusted dependingupon the calculated result from the circuit 39, and whereby the mixtureratio of nitrogen and oxygen is so changed that the composition thereof,that is, the initially selected refractive index is maintained. Hence,refractive indexes of lenses and gases in the optical projection system7 can be maintained constant irrespective of changes in the atmosphericpressure of the environment, and the projection magnification can bemaintained substantially constant.

By maintaining a refractive index constant relying upon the gaseouscomposition, it is possible to maintain constant projectionmagnification as well as focal position. Furthermore, the atmosphericpressure of environment and the focal position can be displayed in realtime on a display panel.

In the foregoing description, the nitrogen and oxygen were used toadjust the refractive index.

In addition to nitrogen and oxygen, however, use can be made of carbondioxide gas, water vapor, helium, neon, argon, and the like, to adjustthe refractive index. Table 1 shows refractive indexes and densities ofthese gases.

                  TABLE 1                                                         ______________________________________                                        Refractive indexes and densities of gases.                                             ← Refractive indexes                                                     using D-ray (λ = 589.3 nm)                                                               Densities (kg m.sup.-3)                                     under 1 atm. at 0° C.                                                                    under 1 atm. at                                    Gases    relative to vacuum                                                                              0° C.                                       ______________________________________                                        Air      1.000292          1.293                                              Oxygen   1.000272          1.429                                              Nitrogen 1.000297          1.250                                              Carbon   1.000450          1.977                                              dioxide                                                                       Water vapor                                                                            1.000252          0.598                                              Helium   1.000035          0.1785                                             Neon     1.000067          0.900                                              Argon    1.000284          1.784                                              ______________________________________                                    

Gases having large refractive indexes and small refractive indexesrelative to air (refractive index, 1.000292) should be selected and usedin combination to adjust the refractive index. By mixing such gases atpredetermined ratios, therefore, the refractive index of the gaseousatmosphere can be controlled. In accordance with the preferredembodiment of the present invention, therefore, use can be made ofcarbon dioxide having a large refractive index, the air having astandard refractive index, and helium gas having a small refractiveindex. With a gaseous mixture consisting of carbon dioxide, air andhelium, the refractive index of the gaseous atmosphere in the light pathin the tube 9 can be easily adjusted to obtain a desired value bychanging the mixture ratio of the gas having a large refractive index,the gas having a standard refractive index, and the gas having a smallrefractive index. More specifically it is possible to adjust therefractive index over a range of from a large value to a small value.There exists a difference of about 40 millibars between the maximumatmospheric pressure and the minimum atmospheric pressure over the wholeyear, i.e., a variation of about ±20 millibars relative to the averageatmospheric pressure. Using the gaseous mixture consisting of carbondioxide, air and helium however, the refractive index can be adjustedover a range of from a large value to a small value. Therefore, evenwhen the atmospheric pressure changes greatly throughout the year, therefractive index can be properly adjusted by adjusting the mixture ofthe gases depending upon the change in the atmospheric pressure.Furthermore, carbon dioxide, air and helium are inexpensive, harmless,and can be easily handled. Moreover, the gaseous mixture consisting ofcarbon dioxide, air and helium does not take part in the chemicalreaction even when it has received optical energy thermal energy fromthe exposure rays, and does not deteriorate or adversely affect thelenses or the tube in the optical system.

According to another embodiment of the invention, the gas is furthersupplied to a place near the lenses in the optical system and to spacebetween the lenses. By supplying gases for controlling the refractiveindex to the place near the lenses and to the space between the lenses,the mixing ratio of gases can be adjusted in such places to cope withthe change in the environmental conditions such as atmospheric pressure,temperature and humidity, in order to obtain predetermined opticalcharacteristics such as refractive index, focal distance, and reductionratio.

The gas supply pipe 33 according to the invention is connected tovarious gas sources via control valves to adjust the flow rates ofgases. The gas supply system from the gas sources to the gas intakeports 30, 32 or to the gas exhaust port 31, controls the gaseouscomposition in the optical projection system 7; hence, substantiallyserves as a light path length setting portion to set the length of thelight path.

A barometer 23 is installed near the exposure body 1, and a control unit38 is provided to control the valves responsive to the detectedatmospheric pressure, so that the flow rates of gases are controlled.The control unit 38 contains an operation circuit 39 which calculatesthe density of the air that varies with the change in the atmosphericpressure. Responsive to outputs of the operation circuit 39, openingdegrees of the valves are adjusted to control the flow rates of gases.

According to this construction, therefore, the gases from the gassources are introduced into the tube 9 through gas supply pipe 33 andgas intake ports 30, 32, and are discharged through gas exhaust port 31and clearance between the wafer 22 and the tube 9. Therefore, the tube9, i.e., the optical projection system 7 is filled with the gaseousmixture, the pressure thereof being equal to, or slightly higher than,the ambient external atmospheric pressure. By mixing the gases in asuitable ratio, the refractive index of the gaseous atmosphere can becontrolled.

The inventors have repeated experiments extensively to determine thecause of change in the reduction ratio (transfer magnification), andhave found that the reduction ratio was directly affected not only byatmospheric pressure but also by ambient temperature and humidity of theenvironment in which the apparatus was installed.

That is, the tube in the optical projection system expands or contractsas temperature changes, so that the size of optical axes of reticle andlens also change thereby changing the reduction ratio. Moreover, themoisture content of the air changes in the optical projection system ashumidity change, and whereby the relative refractive index of the lenschanges so that the reduction ratio changes with the focal distance.

Based upon the results determined by the inventors, there is providedaccording to the present invention an exposure method and an apparatustherefor, in which change in the projecting magnification such asreduction ratio of the transferred pattern is prevented from takingplace irrespective of the change in the environmental conditions such asatmospheric pressure, temperature and humidity, to improve dimensionalprecision of the transferred pattern, so that the pattern can bereproduced very precisely.

The invention comprises, in addition to those mentioned in embodiment 1or 2, detectors such as thermometer and hygrometer to detect thetemperature of the tube of the optical projection system, and to detectthe humidity near the optical system, the detectors being installed nearthe apparatus or directly on the apparatus, and a control unit whichcontrols optical characteristics based upon signals detected by thedetectors. Namely, the control unit adjusts the optical characteristicsdepending upon environmental conditions, so as to adjust variations inthe projection magnification and/or variation in the focal position,i.e., to adjust variation in the optical characteristics, so that thepattern can be reproduced very precisely.

[Embodiment 3]

FIG. 9 shows a further embodiment of the present invention, wherein thesame portions as those of the embodiment of FIG. 4 are denoted by thesame reference numerals. In this embodiment, among the group of lenses6, a moving lens 39 close to the reticle is held by a moving lenssupport 40. The piezo-electric elements 16 are interposed between thetube 9 and the moving lens support 40. The piezo-electric element 16 areprovided with electrodes to which the lead wires are connected. Bysupplying electric current, the piezo-electric element can be expandedor contracted in the direction of optical axis depending upon the amountof electric current.

In a telecentric projecting optical system in which the beam isperpendicularly incident upon the pattern surface, in general, it isdifficult to correct the magnification by moving the reticle up anddown. In such a telecentric projecting optical system, a lens close tothe reticle is moved in the direction of the optical axis to change thereduction ratio. The reduction ratio can be maintained constantirrespective of the change in the atmospheric pressure by detecting theatmospheric pressure using barometer 23, and moving the lens 39depending upon the atmospheric pressure in the direction of opticalaxis.

The invention was concretely described in the foregoing with referenceto embodiments. The invention is concerned with an exposing method andan exposing apparatus. Namely, the invention relates to an exposuremethod wherein at least one of the environmental conditions, i.e., atleast one of atmospheric pressure, temperature and humidity in which theexposure apparatus is placed, is detected, and the refractive index ofthe optical projection system of the exposure apparatus and/or the focalposition are controlled so as to obtain desired values depending uponthe change in the environmental conditions.

According to the exposure method of the invention, composition of thegases in part or whole of the optical projection system is changeddepending upon the change in the atmospheric pressure of theenvironment.

According to the exposure method of the present invention, furthermore,ambient atmospheric pressure is detected as the atmospheric pressure ofthe environment.

The invention further relates to an exposure apparatus comprising: adetecting portion which detects at least one of the environmentalconditions, i.e., at least one of atmospheric pressure, temperature andhumidity in which the exposure apparatus is placed; a light path lengthsetting portion which changes the refractive index of gas in theprojecting optical system in the exposure apparatus to change therelative refractive index of the optical system, in order to change thelength of the optical path; and a control unit which controls the lightpath length setting portion based upon environmental condition signalssuch as atmospheric pressure, temperature and humidity detected by thedetecting portion, and which sets the projecting magnification of thepattern to be projected and/or the focal position to predeterminedvalues.

According to the exposure apparatus of the invention, the light pathlength setting portion is constituted as a gas supply system which formsa predetermined gaseous atmosphere in part of whole of the opticalprojection system.

According to the exposure apparatus of the invention, furthermore,mixing ratio of a plurality of gases is changed by the gas supplysystem, in order to change the refractive index of the gases.

In the exposure apparatus of the present invention, the pressuredetecting portion is a barometer.

Effects of the invention are described below.

(1) Changes in the environmental condition such as atmospheric pressure,temperature and humidity in which the exposure apparatus is placed, aredetected, and the control operation is reliably carried out dependingupon the detected values, so that the refractive index of the projectingoptical system will not be substantially changed. Therefore, theprojecting magnification and/or the focal position are prevented fromchanging irrespective of the change in the environmental conditions, andthe pattern is transferred maintaining high precision.

(2) The apparatus comprises a pressure detecting portion for detectingthe atmospheric pressure of environment, a setting portion forsubstantially setting the length of the optical path in the opticalprojection system, and a control unit which controls the refractiveindex in the optical path length setting portion to a constant valuerelying upon the values detected by the pressure detecting portion.Therefore, the refractive index can be controlled substantially in realtime responsive to changes in atmospheric pressure of the environment,and the projecting magnification can be stably controlled maintaininghigh precision.

(3) The light path length setting portion is set to be substantiallyconstant by changing the distance among the lens, reticle and waferdepending upon the change in the atmospheric pressure of theenvironment. Therefore, magnification can be controlled at high speedsmaintaining high precision. Furthermore, the angle for supporting thereticle can be easily adjusted, making it possible to adjust trapezoidaldeformation.

(4) The light path length setting portion is so constructed as tomaintain a constant refractive index for gas supplied into the opticalprojecting system irrespective of the change in the atmosphericpressure. Therefore, the magnification can be stably controlled, and themethod can be easily adapted to an existing exposing apparatus at areduced cost.

The invention accomplished by the inventors was concretely described inthe foregoing by way of embodiments. The invention, however, should inno way be limited to the above embodiments only but can be modified in avariety of other ways without departing from the spirit and scope of theinvention. For instance, the pressure detecting portion may detect theambient atmospheric pressure, and the atmospheric pressure ofenvironment may be found from the difference between the atmosphericpressure of environment (clean room) which as been determined in advanceand in which the exposure apparatus is placed. Or, magnification may becontrolled depending directly upon ambient atmospheric pressure.

It can also be arranged to maintain the length of the light pathsubstantially constant by controlling the temperature or the humidity inthe optical projecting system, so that the length of the light path ofthe tube is changed by the thermal expansion and the focal distance ofthe lens is changed in the optical system by the water vapor.Theoretically, it is also possible to maintain constant theenvironmental conditions in which the exposure apparatus is placed.This, however, is very expensive and is not practicable.

It is also allowable to utilize a mechanically workingexpanding/contracting mechanism instead of the piezo-electric elementsused in the embodiment 1. In addition to the nitrogen and oxygen used inthe embodiment 2, furthermore, it is permissible to use other gases aswell as combinations with other gases such as CO₂, freon, and the like,as mentioned earlier. It is further possible to supply the gas to aportion of the optical projecting system 7 in the embodiment 2, tocorrect the projecting magnification. This may be combined with thecorrection of focal position of the embodiment 1. Furthermore, since themagnification may often be changed by the change in the environmentaltemperature and humidity, the temperature and humidity may be detectedto control the optical characteristics relying thereupon.

The above description has dealt with the case where the inventionaccomplished by the inventors was adapted to the exposure technique ofthe type of reduced magnification for use in the photolithographytechnique for the semiconductor devices in the field of art that servesas the background of the present invention. The invention, however, isnot limited thereto only but can also be adapted to the exposuretechnique of the type of the same magnification as well as to theexposure technique of the fields other than the manufacture ofsemiconductor devices.

What is claimed is:
 1. An exposure method comprising the steps ofdetecting environmental conditions including at least atmosphericpressure in which an exposure apparatus is placed, and controlling therefractive index of gas in an optical projecting system of the exposureapparatus in dependence upon at least the detected atmospheric pressureto change the relative refractive index of the optical system so as tochange the length of the optical path of the optical system for settingat least one of the projecting magnification of the pattern to beprojected and the focal position to predetermined values.
 2. An exposuremethod according to claim 1, wherein the step of controlling includeschanging compositions of at least one gas in the optical projectingsystem.
 3. An exposure method according to claim 1, wherein the step ofdetecting includes detecting the atmospheric pressure of the open air asthe atmospheric pressure of the environment.
 4. An exposure methodaccording to claim 1, wherein the step of detecting the environmentalconditions further includes detecting at least one of temperature andhumidity.
 5. An exposure apparatus comprising: means for detectingenvironmental conditions including at least atmospheric pressure inwhich the exposure apparatus is placed; a light path length settingmeans for changing the refractive index of gas in an optical projectingsystem in the exposure apparatus to change the relative refractive indexof the optical system so as to change the length of the optical path ofthe optical system; and control means for controlling the light pathlength setting means based upon the signals produced by said detectingmeans and for setting at least one of the projecting magnification ofthe pattern to be projected and the focal position to predeterminedvalues.
 6. An exposure apparatus according to claim 5, wherein the lightpath length setting means is constituted as a gas supply system whichforms a predetermined gaseous atmosphere in at least part of the opticalprojecting system, and the control means changes the gaseous compositionin the optical projecting system.
 7. An exposure apparatus according toclaim 6, wherein the control means changes the mixing ratios of aplurality of gases supplied by the gas supply system in order to changethe refractive indexes of gases.
 8. An exposure apparatus according toclaim 5, wherein the means for detecting the environmental conditionsfurther detects at least one of temperature and humidity.
 9. An exposureapparatus comprising: a barometer which detects the atmospheric pressureof environment in which the exposure apparatus is placed; a light pathlength setting portion which changes the refractive index of gas in theoptical projecting system in the exposure apparatus to change a relativerefractive index of the optical system, in order to change the length ofthe optical path; and a control unit which controls the light pathlength setting portion based upon the atmospheric pressure signalsproduced by said barometer, and which sets the projecting magnificationof the pattern to be projected and/or the focal position topredetermined values; wherein the light path length setting portion isconstituted as a gas supply system which forms a predetermined gaseousatmosphere in part or whole of the optical projecting system, thegaseous composition in the optical projecting system is changed by thecontrol unit, and the mixing ratio of a plurality of gases supplied bythe gas supply system are changed in order to change the refractiveindexes of gases.
 10. An exposure apparatus according to claim 9,wherein adjusting units are installed in the gas supply system to adjustat least one of the temperature and humidity of gases.
 11. An exposureapparatus according to claim 10, wherein a filter is installed in thegas supply system to clean the gases.
 12. An exposure apparatusaccording to claim 9, wherein the plurality of gases supplied by the gassupply system consist of essentially of nitrogen and oxygen.
 13. Anexposure apparatus according to claim 9, wherein the plurality of gasessupplied by the gas supply system consist essentially of carbon dioxide,air and helium.
 14. An exposure apparatus according to claim 9, whereinthe plurality of gases supplied by the gas supply system consistessentially of the air, a gas having a refractive index greater thanthat of the air, and a gas having a refractive index less than that ofthe air.
 15. An exposure apparatus comprising a drive mechanism which isprovided on the body of the exposure apparatus to change the distancebetween a reticle and a lens close to the reticle in the direction of anoptical axis of an optical projecting system; detector means fordetecting environmental conditions including at least atmosphericpressure in which the exposure apparatus is placed; and a control unitwhich controls said drive mechanism based upon the output of saiddetector means to adjust the projecting magnification of the exposureapparatus to a predetermined value.
 16. An exposure apparatus accordingto claim 15, wherein the drive mechanism has three or morepiezo-electric elements that undergo displacement by small amountsresponsive to change of voltage, said piezo-electric elements beingprovided at the lower portion of a support frame to move said supportframe holding the reticle up and down, and said piezo-electric elementsare supplied with the same voltage or different voltages to controlmovement in the up and down direction.
 17. An exposure apparatus forexposing a photoresist film coating on a wafer to a fine pattern on areticle or mask by optically projecting the pattern onto the photoresistfilm comprising: a barometer which detects the atmospheric pressure ofenvironment in which the exposure apparatus is placed; an effectivelight path length setting portion which changes the refractive index ofgas in an optical projecting system in the exposure apparatus to changea relative refractive index of the optical system so as to change theeffective length of the optical light path; and a control unit whichcontrols the effective light path length setting portion based upon theatmospheric pressure signals produced by said barometer, and which setsthe projecting magnification of the pattern to be projected; wherein theeffective light path length setting portion is constituted as a gassupply system which forms a predetermined gaseous atmosphere in at leastpart of the optical projecting system, the gaseous state in the opticalprojecting system being changed by the control unit, and the state of atleast one gas supplied by the gas supply system being changed in orderto change the refractive index at least one of the gas.
 18. An exposureapparatus according to claim 17, wherein adjusting units are provided inthe gas supply system to adjust the temperature and humidity of the atleast one gas.
 19. An exposure apparatus according to claim 17, whereina filter is provided in the gas supply system to clean the at least onegas.
 20. An exposure apparatus according to claim 17, wherein gases aresupplied by the gas supply system and consist essentially of nitrogenand oxygen.
 21. An exposure apparatus according to claim 17, whereingases are supplied by the gas supply system and consist essentially ofcarbon dioxide, air and helium.
 22. An exposure apparatus according toclaim 17, wherein gases are supplied by the gas supply system andconsist essentially of air, a gas having a refractive index greater thanthat of the air, and a gas having a refractive index less than that ofthe air.
 23. An exposure method for exposing a photoresist film coatedon a wafer to a fine pattern on a reticle or mask by opticallyprojecting the pattern onto the photoresist film comprising the steps ofdetecting the change of atmospheric pressure in which an exposureapparatus is placed, and controlling the refractive index of an opticalprojecting system of the exposure apparatus in accordance with thedetected change to adjust the projecting magnification of the projectedpattern to predetermined values.
 24. An exposure method according toclaim 23, wherein the step of controlling includes changing compositionsof gases in at least part of the optical projecting system dependingupon the change of atmospheric pressure.
 25. An exposure methodaccording to claim 23 wherein the step of detecting includes detectingthe atmospheric pressure of the open air as the atmospheric pressure ofthe environment.
 26. An exposure apparatus for exposing a photoresistfilm coated on a wafer to a fine pattern on a reticle or mask byoptically projecting the pattern onto the photoresist film comprising:detecting means for detecting the atmospheric pressure in which theexposure apparatus is placed, an effective light path length settingmeans for changing the refractive index of gas in an optical projectingsystem in the exposure apparatus to change the relative refractive indexof the optical system so as to change the effective length of theoptical light path; and control means for controlling the effectivelight path length setting means in accordance with signals produced bysaid detecting means and for setting the projecting magnification of thepattern to be projected to predetermined values.
 27. An exposureapparatus according to claim 26, wherein the effective light path lengthsetting means is constituted as a gas supply system which forms apredetermined gaseous atmosphere in at least part of the opticalprojecting system, and the control means changes the gaseous compositionin the optical projecting system.
 28. An exposure apparatus according toclaim 27, wherein the control means changes the mixing ratios of aplurality of gases supplied by the gas supply system in order to changethe refractive indexes of gases.
 29. An exposure apparatus for exposinga photoresist film coated on a wafer to a fine pattern on a reticle byoptically projecting the pattern onto the photoresist film comprising: adrive mechanism which is provided on the body of the exposure apparatusto change the distance along an optical axis between a reticle and alens close to the reticle in an optical projecting system; detectormeans for detecting atmospheric pressure in which the exposure apparatusis placed; and control means for controlling said drive mechanism basedupon the output of said detector means to adjust the projectingmagnification of the exposure apparatus to a predetermined value.
 30. Anexposure apparatus according to claim 29, wherein the drive mechanismhas at least three piezo-electric elements that undergo displacement bysmall amounts responsive to change of voltage, said piezo-electricelements being provided at the lower portion of a support frame to movesaid support frame holding the reticle up and down, said piezo-electricelements being supplied with the same voltage or different voltages tocontrol movement in the up and down direction.
 31. An exposure methodcomprising the steps of detecting a change of environmental conditionsincluding at least atmospheric pressure in which an exposure apparatusis placed, and controlling at least one of the refractive index of anoptical projecting system of the exposure apparatus and the position ofan optical axis of the exposure apparatus to adjust at least one of theprojective magnification of the projected pattern and the focal positionto desired values in accordance with the detected change, the step ofcontrolling including changing compositions of gases in the opticalprojecting system depending upon the detected change of theenvironmental conditions.
 32. An exposure apparatus according to claim31, wherein the step of detecting includes detecting the atmosphericpressure of the open air as the atmospheric pressure of the environment.33. An exposure method according to claim 31, wherein the step ofdetecting the environmental conditions further includes detecting atleast one of temperature and humidity.